In ink-jet printing, ink is ejected from a narrow orifice in the direction of a substrate. In one type of ink-jet printing, known as drop-on-demand printing, the ink is ejected in a series of drops. The drops may be produced and controlled using a piezoelectric ink-jet head that has a large number of orifices. Each orifice is separately controllable to selectively eject ink at desired locations, or pixels, of the image. For example, an ink-jet head may have 256 orifices that have spacing for a printing resolution of at least 100 pixels (dots) per inch (dpi) and sometimes far more than that. This dense array of orifices allows complex, highly accurate images to be produced. In high performance print heads, the nozzle openings typically have a diameter of 50 microns or less (e.g., around 25 microns), are separated at a pitch of 25–300 nozzles/inch, have a resolution of 100 to 3000 dpi or more, and provide drop sizes of about 1 to 70 picoliters (pl) or less. Drop ejection frequency is typically 10 kHz or more. A drop-on-demand piezoelectric print head is described in U.S. Pat. No. 4,825,227, the entire content of which is incorporated herein by reference.
“Cockle” or “cockling” refers to a morphological change (e.g., a dimensional change) in an area of a print substrate caused by the substrate's interaction with ink. Substrate cockle can be detrimental to image quality. One approach used in the office printer field to prevent image distortion effects related to cockle is to limit the coverage of ink disposed on the substrate so that any subsequent cockling minimally distorts the substrate. However, this approach can be limiting, especially in applications requiring high-resolution full-color images. Another approach to the problem of cockle distortion is to use a coated or treated substrate. These substrates typically include additives such as clay, silica, or other materials to produce a glossy paper and inhibits volume-changing interactions with ink, thereby preventing cockling. Coated papers are commonly used in commercial photo ink-jet printers, which produce high-resolution full-color images over, for example, a 6 inch×4 inch or larger area.
Commercial printing is commonly done on multi-color continuous web printing presses. The web, provided, e.g., as a roll of paper, is directed along a paper path that includes separate stations for each color. The web is then slit into sheets and stacked.